Turning to FIG. 1 of the drawings, the reference numeral 100 generally designates a conventional charge sharing circuit. Circuit 100 generally comprises current source 102, diodes D1 and D2, resistor R1, switch 51, and NPN transistor Q1. Diode D1 is coupled between output pin OUT and the emitter of transistor Q1, while diode D2 is coupled between input pin IN and the collector of transistor Q1. Switch S1 and a current source 102 are coupled in series between the base of transistor Q1 and a voltage supply (which provides a supply voltage VP). Additionally, resistor R1 is coupled between the base and emitter of transistor Q1. If the switch 51 is closed (conducting) a current can flow from the input pin IN to the output pin OUT through diodes D1 and D2 as well as the channel of the transistor Q1. Otherwise, current does not flow from the input pin IN to the output pin OUT when switch S1 is open.
This circuit 100, however, has several disadvantages. For example, circuit 100 employs bipolar transistors, which are not available in many CMOS processes. Furthermore, there can be a charge injection from the power supply (which supplies voltage VP) to the output pin OUT that can reduce the efficiency of the circuit and the charge can only flow in one direction.
Therefore, there is a need for an improved charge sharing circuit.
Some examples of other conventional circuits are: Japanese Patent Appl. No. JP09-027,742; and U.S. Pat. No. 5,574,633.